Display screen or portion thereof with a graphical user interface of a mobile device



FIG. 1 is a front view of a first embodiment of a display screen with a graphical user interface of a mobile device; and,

FIG. 2 is a front view of a second embodiment of a display screen with a graphical user interface of a mobile device.

The broken lines illustrating components of a web page are for illustrative purpose only and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface of a mobile device, as shown and described. 